Prausnitz-kustner (PK) reaction was used to demonstrate -
High-Yield Explanation
Ans. is 'd' i.e., IgE o IgE is homocytotropic i.e. species specific. Only human IgE can fix to the surface of human cells. This is the basis of the Prausnitz-Kustner (PK) reaction, which was the original method for detecting atopic antibody.